shimano K cassette (13~34t) Or 13-26 if no low gears needed or a sun race (brand) freewheel.. If a screw on Freewheel
Plus a new KMC chain in either case .
It will be more than your
Dream budget cap.
try to keep it under 30 bucks i paid 60 for the bike
good luck with that .. all you can do is look for another Junque Bike to cannibalize then..